The present invention relates to containers, such as bottles or flasks, of a heterogeneous structure made from a material which produces a barrier effect and a polymer material.
The disadvantage of containers made from a polymer material such as PET is that they are not impermeable to certain gases, particularly oxygen and carbon dioxide.
This is the reason why carbonated drinks gradually lose their carbon dioxide to the air through the polymer substance: the shelf life of a carbonated liquid contained in a PET bottle will not be more than a few weeks in terms suitability for sale or at most a small number of months (for example 4 to 6).
This is also the reason how oxygen in the air is able to penetrate the polymer material to come into contact with the liquid in the container, placing it at risk of oxidation accompanied by a deterioration in its properties: the shelf life of a bottle made from PET and filled with beer will not be more than a few weeks (for example 2 to 5 weeks) in terms of suitability for sale.
A known approach to this problem is to enhance the natural barrier effect of the polymer substances used to make the containers by lining the polymer wall with a layer of material which has a stronger barrier effect.
Accordingly, it has been proposed that synthetic materials in multiple layers be used for this purpose, such as those based on aliphatic polyamides and/or mixtures of different substances. The containers are then made using multi-layered preforms, in which the layer of material with a barrier effect is located between at least two layers of polymer material (for example PET). Beer bottles made in this manner will have a considerably longer shelf life (for example up to 12 months).
However, one major disadvantage of these multi-layered containers is that the layers will come unstuck from one another. In addition, making the preform, as well as making the container from the preform by blow-moulding or by stretching-blow-moulding, are quite complex processes and require certain precautions, which makes them expensive.
Another proposal is that polymer containers be treated by applying an external coating of an appropriate material such as those known as PVDC or thermo-setting resins. However, the gain in barrier effect achieved as a result is still quite low and the presence of the coating material leads to difficulties when it comes to recycling the basic polymer material.
Moreover, in all the known solutions mentioned above, the polymer material (for example PET) is left in contact with the liquid and does not offer any protection against the disadvantages incurred by this contact: possibility of certain constituents migrating from the polymer into the liquid, possibility of a chemical reaction between the polymer and liquid, acetaldehyde being transferred into the liquid, etc., all factors which are likely to give rise to organoleptic problems.
It has also been proposed that a layer of material with a barrier effect, for example hard carbon, be applied to a wall made from polymer, for example PET, using plasma (document U.S. Pat. No. 5,041,303).
Document EP 0 773 166 also mentions the possibility of forming such a layer of carbon on the internal face of the container wall.
A carbon layer deposited in this manner would, of course, remedy all the disadvantages listed above.
However, a relatively thick layer of hard carbon or diamond-like carbon (DLC) would be needed. The wall of a container made in this way would therefore have an internal layer of hard carbon DLC, which is quite rigid, and an external layer of polymer material such as PET, which is highly deformable. Due to their differing and incompatible mechanical properties, the two layers of polymer and hard carbon end up coming apart or unstuck.
Generally speaking, polymer containers with a barrier effect by implementation of one of the techniques mentioned above are not very common due to the complexity inherent in the different processes, low production rates and the high cost of manufacturing methods of this type.
The object of the invention is substantially to remedy simultaneously all the problems mentioned above, as encountered with known containers with an improved barrier effect, and to propose a container which will effectively protect its contents whilst being easy to manufacture on an industrial scale, using less complex means under acceptable economic conditions.
To this end, in a first aspect, the invention proposes a container such as a bottle or flask, heterogeneously made from a material with a barrier effect and a polymer material which, as proposed by the invention, is characterised in that the material producing the barrier effect consists of an amorphous carbon material with a polymer tendency, which is applied to a substrate of polymer material. The substrate is a blank of the container and already has the final shape of the container.
By amorphous carbon material with a polymer tendency is meant carbon containing not only CH and CH2 bonds found in the hard carbon, but also CH3 bonds which are absent in hard carbon (to get a rough idea, the proportions of CH3, CH2 and CH are respectively 0, 40 and 60 in hard carbon and 25, 60 and 15 in amorphous carbon with a polymer tendency, whereas the proportions of the electronic states sp3, sp2 and sp are respectively 68, 30 and 2 in hard carbon and 53, 45 and 2 in carbon of the polymer type).
Choosing an amorphous carbon material with a polymer tendency overcomes the problem caused by the rigidity of hard carbon or DLC: in practice, amorphous carbon materials with a polymer tendency have a substantially lower mechanical rigidity than that of hard carbon and the deformation capacity of a layer of such a material is comparable with that of a polymer such as PET: a container wall made as proposed by the invention using such an amorphous carbon material with a polymer tendency adhered to a substrate of polymer material such as PET will therefore be able to withstand deformation at normal levels without these two layers coming unstuck.
It is true that inherent in their physical and chemical structure, amorphous carbon materials with a polymer tendency have a lower molecular permeability coefficient than hard carbon which has been used to date and it was thought that any barrier effect they produced was less than perfect. This is one reason why they have not been considered until now and why hard carbon or DLC was used to provide layers with a barrier effect. Surprisingly, tests conducted with amorphous carbon materials with a polymer tendency have shown that the barrier effect obtained under certain operating conditions is generally sufficient in practice for use in the packaging of carbonated liquids or oxidizable liquids.
It would also be conceivable to use carbon-type nano-composites (or DLN)xe2x80x94i.e. composites with reciprocally interleaved dual networks, stabilised and random, one of which is a network of amorphous carbon with a polymer tendency (a-c:H, with up to 50% sp3 bonds) whilst the other may be a network of silicon stabilised by oxygen (a-Si:o)xe2x80x94and nano-composites incorporating metal atoms.
It is of advantage if the coating of amorphous carbon material with a polymer tendency is of a thickness less than approximately 3000 xc3x85 (beyond that, too great a thickness imparts too high a mechanical rigidity to the carbonated coating, with the risk that it will rupture or become unstuck), preferably between 800 and 1500 xc3x85.
It should be pointed out that, although still transparent at the above-mentioned thicknesses, amorphous carbon of the polymer type is amber in colour which helps to protect against ultraviolet rays (as a protection for beer in particular). It has been found that under certain operating conditions, the effectiveness of the barrier against ultra-violet afforded by this protection depends on the thickness of the coating and, interestingly, increases sharply with the intensity of ambient light (factor of about 8 in darkness but a factor of about 30 in daylight).
The polymer material, which in practical applications is a polyolefin or a polyester such as PET or PEN, may be used in a reduced thickness because of the natural rigidity of the carbon layer. On this subject, it should also be pointed out that the carbon-based coating helps to reduce deformation of the container wall when subjected to the pressure of a gaseous liquid, such as a carbonated liquid. The container therefore retains a stable shape and its interior volume remains constant: there is no change in the composition of the liquid contained in it.
Although the coating with the barrier effect may be provided on the exterior of the container blank, it is nevertheless preferable if this coating forms the internal coating of the container so that it will help to isolate the polymer material and the liquid held in the container: the barrier effect will therefore be extended and will render any migration of the polymer constituents into the liquid, any chemical reaction between the substances in the polymer and the liquid and any migration of acetaldehyde into the liquid, etc., impossible.
It should be stressed, at this point, that the principle underlying a container made as proposed by the invention is that chemical bonds are established between the superficial carbon atoms of the polymer substrate which have a free chemical bond and the atoms of the carbon material which are brought into contact with the polymer and have a free chemical bond, ready to combine with the free bond of the superficial carbons in the polymer substrate. Under these conditions, the coating of carbon material is linked to the polymer substrate by a chemical and hence extremely powerful bond; since the carbon material also has a polymer tendency as explained above, the powerful chemical bond is nevertheless accompanied by a relative capacity for deformation in the carbon coating, these two features together providing a structure which no longer exhibits the disadvantages (layers becoming unstuck in particular) of the known containers made from hard carbon or DLC.
A plasma deposition process can be used to deposit the carbon coating, with carbon atoms having a free chemical bond available for bonding with that of a superficial carbon atom in the polymer.
Accordingly, a second aspect of the invention relates to a method using a plasma excited by an electromagnetic wave to form a container, such as a bottle or flask, made heterogeneously from a material with a barrier effect and a polymer material forming a substrate conforming to the shape of said container to be produced, characterised in that said polymer material forming the substrate is coated with a material with a barrier effect comprising an amorphous carbon material with a polymer tendency, consisting of two steps:
a blank of the container made from a polymer material forming the above-mentioned substrate is placed in an enclosure,
at least one carbon precursor is injected into the reaction chamber in the gaseous state at a very low pressure of less than 10 mbar, the precursor being selected from the alkane, alkene, alkyne and aromatic compounds or a combination of some of them,
a microwave in the UHF range is electromagnetically excited in the reaction chamber with a relatively low power sufficient to generate a plasma under temperature conditions which will maintain the polymer at a temperature below the glass transition temperature on the one hand and which will cause an amorphous carbon material with a polymer tendency to be deposited on the other.
In a first possible implementing method, the container blank made from polymer is closed whilst the gaseous carbon precursor is being injected into the enclosure which is then the reaction chamber, whereby the coating of amorphous carbon material with a polymer tendency is deposited on the external surface of the container blank.
In a second possible implementing method, the gaseous carbon precursor is introduced inside the container blank of polymer material, which then becomes the reaction chamber, whilst simultaneously creating a pronounced vacuum in the container blank, whereby a plasma is formed in the interior of the blank only and the coating of amorphous carbon material with a polymer tendency is deposited on the internal surface of the container blank; furthermore, in order to prevent the container from deforming due to the prevailing vacuum, a vacuum is simultaneously generated in the enclosure to reduce the pressure differential between the interior and the exterior of the blank. Moreover and by preference in this instance, the enclosure is of a transverse dimension close to that of the body of the container blank, closely conforming to the container blank, so that a means with a lower power rating can be used to generate the vacuum.
As a result of the features characterising the method proposed by the invention, a coating of amorphous carbon material with a polymer tendency can be deposited at the requisite low thickness of less than 3000 xc3x85 and in particular between 800 and 1500 xc3x85 in a short time of a few seconds and not more than about twenty seconds, with a modest microwave power in the order of a few hundred watts (for example about 200 to 600 W) producing a power density of about 0.5 to 2 watts per cubic centimeter. As a result, the corresponding increase in temperature within the polymer material of the container blank forming the substrate on which the carbon coating will be deposited (inside or outside, as is the case) remains relatively low and below the glass transition temperature of the polymer (approximately 80xc2x0 C. in the case of PET).
These are the conditions under which the carbon coating is formed under the action of a microwave plasma at low pressure (not exceeding a few millibars and in practice in the order of 0.01 and 0.5 mbar) or xe2x80x9ccold plasmaxe2x80x9d, causing an amorphous carbon structure with a polymer tendency to be formed, i.e. consisting of or containing an over-hydrogenated amorphous carbon network exhibiting the advantageous properties listed above.
Apart from obtaining a container with a barrier effect which is mechanically well bonded onto the polymer substrate, the method proposed by the invention offers the notable advantage of facilitating the manufacture of sterile containers which may be used in aseptic packaging production lines.
The plasma generated during the process of depositing the carbon coating is sufficient to clean the internal surface of the container blank as desired.
In order to obtain a more intense aseptic effect, it would be conceivable to use a bactericidal agent beforehand, atomised to produce micro-droplets or introduced in vapour form, for example with a bubble system, onto the internal surface of the container blank (for example hydrogen peroxide, phosphoric acid, steam, etc.); subsequent generation of a plasma under the above-mentioned conditions will create a highly reductive medium (by generating native oxygen for example) which is capable of reducing the initial bacterial contamination so as to meet the sterilisation requirements.
In implementing the method described above, a third aspect of the invention is an apparatus which uses a plasma excited by electromagnetic wave to form a container, such as a bottle or flask, made heterogeneously from a material with a barrier effect and a polymer material forming a substrate (container blank) having the shape of said container to be produced, this apparatus comprising a plasma-generating device with an enclosure fitted with means for injecting a gaseous precursor and electromagnetic excitation means, which apparatus is characterised in that in order to coat said polymer material forming the substrate with a material having a barrier effect comprising an amorphous carbon material with a polymer tendency, the means for injecting the precursor are connected to a means for generating a precursor in the gaseous state, selected from the alkane, alkene, alkyne and aromatic compounds or a combination of some of them, in that in order to coat said polymer material forming the substrate with a material having a barrier effect comprising an amorphous carbon material with a polymer tendency, the injection means open into the enclosure and are designed to deliver the gaseous precursor at a very low pressure of less than 10 mbar, and in that the electromagnetic excitation means are of a sufficient rating to generate microwaves in the UHF range.
In a first embodiment, the dimensions of the enclosure are substantially larger than those of the container blank to be treated and injection means open into the enclosure outside the container blank, whereby, the container blank being closed, the apparatus generates a plasma outside the container blank and it is on the external surface of the container blank that the coating of amorphous carbon material with a polymer tendency is deposited.
In a second embodiment, the means for injecting the gaseous precursor open into the interior of the container blank arranged in the enclosure and pumping means are provided opening into the container blank and capable of generating a pronounced vacuum therein, whereby the plasma is generated inside the container blank and it is on the internal surface of the container blank that the coating of amorphous carbon material with a polymer tendency is deposited. In order to prevent the blank from deforming due to the vacuum prevailing in the interior, a vacuum is simultaneously created inside the enclosure to reduce the pressure differential between the interior and the exterior of the blank. Advantageously in this case, the enclosure is provided with a removable cover producing a tight seal, designed to support the injector for the gaseous precursor and the suction orifice of the pumping means; it also has support means designed to support a container blank by the neck thereof, applying the lip of said container blank against the interior face of said cover, surrounding said suction and injector orifices. It is also desirable to be able to displace the support means axially in order to apply the container blank against the interior face of the cover, capping said suction and injector orifices prior to depositing the coating, or in order to remove the finished container once the coating has been deposited.
By preference, in order to facilitate use of the pumping means and avoid having to use means of a higher capacity than necessary, the enclosure has a transverse dimension close to that of the body of the container blank.
As a result of the features proposed by the invention, in particular due to the reduced processing times, it is possible to mount a method of manufacturing a container with a barrier effect on an industrial scale, which will enable containers to be produced at a rate compatible with current requirements for packaging liquids.